The building in Cowpark townland, in the parish of Kilcornan, sits on a north-south ridge overlooking a stream, its walls standing to their full original height and finished at the top with a parapet wall-walk, the kind of protected walkway more commonly associated with tower houses than places of worship. Drainage holes punctuate the parapet at regular intervals. The narrow windows and the box-like bell-cote projecting from the west gable on pyramidal corbels give the whole structure what the archaeologist Peter Harbison, writing in 1970, described as an almost military appearance. An L-shaped slot inside the apex of the west gable once held the rope by which someone standing in the nave could ring the bell above.

The church is dedicated to St Cornan, whose name survives in the parish name Kilcornan. When Ordnance Survey officers gathered local traditions in 1840, they recorded the belief that this Cornan was the same man who served as abbot of Lismore and whose feast day fell on the first of January. The building itself, however, is considerably later than any early medieval foundation: it dates to the fifteenth or sixteenth century, built in limestone rubble with long and short alternating quoin stones at the corners and a pronounced base batter, a sloping thickening of the wall at its foot that adds both stability and that fortress-like solidity. Inside, the east wall retains a scar where a stone altar once stood; one block of it still protrudes from the wall. Beside that altar position, a square aumbry, a small wall-recess used for storing sacred vessels, now shelters the stone roof finial, its socket for a cross still clearly visible. A quatrefoil-shaped piscina, a shallow basin used for rinsing liturgical items, survives at the south-east corner. The church was repaired in the 1930s under the direction of Canon Wall, during which the stones forming one of the windows were recovered and reinstated.

The site is recorded as National Monument No. 345. The church is aligned roughly east-north-east to west-south-west and the first-edition Ordnance Survey six-inch map shows a square graveyard adjoining the south side, which was reused as a children's burial ground, though this enclosure does not appear on later map editions. Visitors who look carefully at the south doorway will notice the drawbar slot inside the entrance and traces of wicker centring still visible in the arch, a survival of the original construction method in which woven rods supported the wet mortar until it set. On the east side of the south doorway, a rough ogee-headed water stoup is set into the wall. Evidence of internal lime render remains on the walls, best preserved at the east end of the north wall, giving some sense of how the interior would once have appeared.